Remove all custom JSON marshaling

[aaronc]

This just causes problems with proto JSON. All of the vesting account custom JSON was removed in #6859. We should probably do an audit and remove any other custom JSON marshaling we can find (and probably YAML too).

This may unfortunately cause some breakage for uses of the legacy REST endpoints, but I don't really see a way around it and it is part of the path towards stable formats.

What do you think @alexanderbez ?

[alexanderbez]

What exact problems does it cause? I don't think we have much custom JSON serialization, so that should be fine. I also don't think we have any custom YAML, but if we do, that's OK to remove IMHO.

[aaronc]

It appears to be causing some of the sim export issues in #6859. Basically jsonpb does some custom stuff because of it but only on one side of marshal/unmarshal. So exported genesis json can't be imported.

[tac0turtle]

I believe the yaml will need to be removed in the near future anyways. The gogoproto extension to add it will not be supported in the new generator

[tac0turtle]

we need to look at removing all calls in the proto files to (gogoproto.jsontag) . With the amino work there may not be a need for these anymore

[tac0turtle]

closing in favour of #8952